Condition responsive switch mechanism

ABSTRACT

A condition responsive electric switch mechanism includes a switch having open and closed positions. A switch actuator is connected to the switch for moving it between its open and closed positions and a spring assembly is connected to the actuator for moving it between the switch open and closed positions. A thermally responsive mechanism, including a sealed expansible chamber assembly, is connected to the switch actuator for controlling movement between the switch open and closed positions. The sealed expansible chamber assembly is partially filled with liquid and partially filled with vapor so that the change in vapor volume between the switch open and closed positions is relatively large as compared to the total vapor volume. The mechanism may include two sets of spring contacts, each with its own actuator. A toggle mechanism is provided to operate one actuator. There is an operator to engage the toggle mechanism for movement of the toggle mechanism between open and closed positions of one set of contacts. There is a manually adjustable support and a spring mounted between the support and the operator. The thermally responsive expansible chamber assembly also engages the operator. The manually adjustable support has a position engaging both actuators for manually opening both sets of contacts.

United States Patent Thompson [4 Apr. 4, 1972 [54] CONDITION RESPONSIVESWITCH 57 ABSTRACT MECHANISM A condition responsive electric switchmechanism includes a 72 Inventor; Paige w Thompson, Morrison, 1 switchhaving open and closed positions. A switch actuator is I connected tothe switch for moving it between its open and Asslgnee: General ElecmcCompany closed positions and a spring assembly is connected to the ac-[22] Filed: May 12 1970 tuator for moving it between the switch open andclosed positions. A thermally responsive mechanism, including a sealedPP 36,624 expansible chamber assembly, is connected to the switchactuator for controlling movement between the switch open and closedpositions. The sealed expansible chamber assembly is g "337/317" 2355:partially filled with liquid and partially filled with vapor so that[58] Fleid 326 327 the change in vapor volume between the switch openand closed positions is relatively large as compared to the total vaporvolume. The mechanism may include two sets of spring [56] Relerencescued contacts, each with its own actuator. A toggle mechanism is UNITEDSTATES p provided to operate one actuator. There is an operator toengage the toggle mechanism for movement of the toggle 3,065,323 ll/l962Grnnshaw ..337/327 mechanism between open and closed positions of oneSet of 13; 3 2 contacts. There is a manually adjustable support and aspring onneger mounted between the support and the operator. Thethermally responsive expansible chamber assembly also engages theoperator. The manually adjustable support has a position engaging bothactuators for manually opening both sets of contacts.

PATENTEDAFR 4 1912 3. 654, 578

sum 2 OF 2 FIG/1- INVENTOR.

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BACKGROUND OF THE INVENTION This invention relates generally to animproved condition responsive electric switch mechanism such asthermostat units for use in connection with heating and coolingapparatus.

Some conventional thermostats for heating and cooling applicationsincorporate a temperature responsive sealed vaporfilled bellows assemblyand a spring, acting in opposite directions on an operating member whichactuates the switch contacts, the operating member being moved first andsecond positions in response to expansion and contraction of the bellowsin response to temperature changes. In order to provide a differentialbetween the temperatures at which the switch contacts are respectivelyopened and closed, a spring mechanism is conventionally provided whichacts upon the operating member and produces a snap action movement ofthe member between its two extreme positions.

One long-standing problem with such mechanisms has been the high levelof noise produced during operation. US Pat. No. 3,354,280 issued to JohnL. Slonneger on Nov. 21, 1967, and assigned to General Electric Company,assignee of the present invention, shows and describes a conditionresponsive switch mechanism which provides the desired quick actioncoupled with quiet operation. The aforesaid US. Pat. No. 3,354,280 isincorporated herein by reference.

The Slonneger mechanism utilizes thermal damping to control the velocityof the snapping mechanism and thus the noise. The exemplificationmechanism shown in the Slonneger patent includes a sealed expansiblechamber, such as a bellows, and an attached tube. The bellows and tubeare connected by a section of tubing of low thermal conductivity. Theentire assembly is filled with an expansible fluid which is part liquidand part vapor, with the liquid being in the tube. In addition to theusual preheater, adjacent the tube, there is a separate bias heater toinsure the bellows temperature remains above the tube temperature. Whilethe arrangement shown in the Slonneger patent provides excellent noisecontrol through the use of thermal damping," it is somewhat complicatedin construction and operation. This construction adds to the cost ofsuch devices and requires care in manufacture, shipping, installationand operation to insure the liquid remains in the tube.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto provide an improved condition responsive electric switch mechanism.

Another object of this invention is to provide an improved conditionresponsive switch mechanism which controls the noise of operation bythermal damping."

Still another object of this invention is to provide such an improvedswitch mechanism which is simple in construction and operation. 1

In carrying out the invention, in one form thereof, I provide acondition responsive electric switch mechanism including a switch meanshaving open and closed positions. Switch actuating means is connected tothe switch means and is movable between first and second positions foroperating the switch means between its open and closed positions. Springmeans is connected to the switch actuating means for transferring theswitch means between open and closed switch positions. Thermallyresponsive means, including a sealed expansible chamber assembly, isconnected to the switch actuation means for controlling movement of theswitch actuation means between its first and second positions inresponse to first and second predetermined temperatures. The sealedexpansible chamber assembly is partly filled with liquid and partlyfilled with vapor such that the change in the volume of vapor as theswitch actuating means moves between its first and second positions isrelatively large as compared to the total vapor volume for producingthermal damping to control the velocity of the switch actuating means asit travels between its first and second positions.

2 BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and otherfeatures and objects of this invention and the manner of attaining themwill become more apparent and the invention itself will be betterunderstood by reference to the following description taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational view of a condition responsive switchmechanism illustrating one form of the present inven tion, with thecover and operating knob removed;

FIG. 2 is a plan view of the switch portion of the mechanism, generallyas seen along line 22 in FIG. 1 and with the switch housing coverremoved;

FIG. 3 is an enlarged, cross-sectional view of the bellows assemblyincluded in the switch mechanism of FIG. 1; and

FIG. 4 is a cross-sectional view of the exemplification conditionresponsive switch mechanism generally as seen along line 4-4 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingsthere is shown an exemplification thermally responsive switch mechanismin the form of a thermostat generally indicated at 10. Such anexemplification thermostat normally would be used for purposes such ascontrolling the heating and cooling of a house, for example. Thesethermostats normally include elements such as cover plates and controlknobs which have been omitted from the drawings for ease of illustratingvarious operating components of the switch mechanism.

The thermostat 10 includes a base 11 having a cavity 12 formed in itsupper surface. A switch housing cover 13 is removably attached to thebottom surface of the base 11 and, with the base 1 1, forms a cavity 14.Two sets of stationary and movable contacts 15, 16 and 17, 18respectively are positioned in the cavity 14. Stationary contact 15 ismounted to a bus bar element 19 to which a first terminal 20 isconnected. Movable contact 16 is mounted on a resilient or springcontact strip 21 which is secured to a bus bar element 22. A secondterminal 23 is connected to the bus bar element 22. Similarly,stationary contact 17 is connected to a bus bar element 24 to which isconnected a terminal 25; and movable contact 18 is mounted on aresilient contact strip 26 which is secured to a bus bar element 27, towhich a tenninal 28 is connected. The set of stationary movable contacts15, 1 6 are utilized to provide a temperature responsive cycling controlwhile the contacts 17, 18 are used in conjunction with the contacts 15,16 to provide a manual off position.

A generally U-shaped frame 29 is attached to the base 11 by somesuitable means such as rivets 29a and forms a support for othercomponents of the switch mechanism. A manually adjustable support in theform of a cam follower 30 is positioned within the frame 29 with one endpivotally seated on a pair of ears 31, provided in the frame 29, and itsother end 32 cooperatively engaging a cam 33. The cam 33 includes asloped cam surface 34 for selectively varying the position of the camfollower 30 and a notch 35 for positioning the cam follower somewhatremoved from the range provided by the cam surface 34. The cam isfixedly attached to a shaft 33a so that as the shaft is rotated by acontrol knob (not shown) different portions of the sloped surface 34 orthe notch 35 are selectively brought into engagement with the end 32 ofcam follower 31).

The cam follower 30 is provided with a recessed seat 36 in which ismounted one end of a range spring 37. The other end of the range spring37 bears against a collar 38 which is threadily received about anoperator 39, in the form of an altitude rod. One end 41 of the operator39 is received in a cupshaped recess 42 in a bellows 43. The other endof the bellows is sealed to a mounting cup 44 by some suitable meanssuch as solder 45, and the mounting cup 44 is attached to the frame 29.The bellows is provided with a short fill tube 46 which is pinched off,or otherwise suitably sealed, as at 47 once the bellows has beenprovided with a suitable charge of fluid. A fluid tight seal is providedbetween the tube 46 and cup by crimping over the tube and the use of anadditional body 48 of solder.

With this arrangement a force is exerted on the operator 39 which is, inefi'ect, the net force of the spring 37 and the bellows 43, which act onthe operator 39 in opposite directions. The effective net force for anyparticular condition of the fluid within the bellows may be varied forcalibration by adjusting the position of the collar 38 on the altituderod or operator 39. This calibration is done by rotating the altituderod relative to the collar 39. For this purpose, the end of the altituderod removed from the bellows is provided with a slot 49 by which the rodmay be rotated by some suitable means such as a screwdriver.

The thermostat also includes a toggle mechanism generally indicated at50. The toggle mechanism includes an arm 51 having one end 52 pivotallymounted on a finger 53 connected to the frame 29 and the other end 54pivotally connected to a return bent toggle spring 55. The other end ofthe toggle spring 55 is pivotally connected to a follower 56 which isslideably mounted in a recess 57 formed between the base 11 and frame29. The follower 56 is threadily engaged by an adjustment screw 58which, in turn, is captured in a slot 59 in the frame 29. Thus, as thescrew 58 is rotated, the follower 56 is moved axially through the slot57 to adjust the tension in the toggle spring 55. The toggle springbiases the end 54 of the arm 51 to the left (as seen in FIG. 1) with anegative gradient force. That is, the force in the direction of movementat the end of the arm 51 becomes greater the farther to the left (asseen in FIG. 1) the end 54 moves.

The operator or altitude rod 39 is formed with a shoulder 60 whichengages the arm 51 intermediate its end to transfer the net effectiveforce of the bellows 43 and range spring 37 to the pivoted arm 51. Infact the shoulder 60 engages a very weak centering spring 61 which isattached to the arm 51 which prevents the edge of the altitude rodpassing through the pivoted arm 51 from engaging the edge of the opening62, which would be detrimental to proper operation of the device.

With this arrangement of parts the toggle spring 55 biases the arm 51 tothe left as seen in FIG. 1 until such time as the net effective force ofthe range spring 37 and bellows 53 is sufficient to overcome this forceand pivot the arm 51 to the right (as seen in FIG. 1) to the full lineposition of FIG. 1. It will be understood that once the net effectiveforce exerted by the operator 39 becomes sufficiently large to overcomethe toggle mechanism and begins to pivot the arm 51 in the clockwisedirection the decreasing force exerted by the toggle spring will tend tocause the arm 51 to snap through to the position shown in FIG. 1. On theother hand when the net effective force exerted through the operator 39becomes insufficient to hold the arm 51 in the position shown in FIG. 1the toggle spring 55 will tend to snap the arm 51 in a counterclockwisepivoted movement.

This movement of the pivoted arm 51 is utilized to control the openingand closing of contacts and 16. To this end an actuator 65 includes ashoulder 66 bearing against the resilient contact strip 21, with a smallextension 67 extending through the strip for insuring constantengagement of the actuator 65 with the resilient contact strip 21. Theactuator 65 includes a second shoulder 68 which engages the pivoted arm51 and a reduced diameter extension 69 which slideably projects throughan opening (not shown) in the arm 51 into proximity with the camfollower 30. The resiliency of the contact strip 21 maintains theshoulders 66 and 68 in engagement with the strip 21 and arm 51respectively. As the arm 51 is pivoted in a clockwise direction to theposition shown in FIG. 1, the actuator 65 moves the resilient contactstrip 21 so as to separate the contacts 15, 16. As the pivoted arm 51 ispivoted in a counterclockwise direction away from its position shown inFIG. 1, the actuator 65 allows the resilient contact strip to return toa position in which the contacts 15, 16 are closed.

Thus as the temperature of the fluid within the bellows changes about apredetermined operating point, which has been calibrated by thepositioning of the altitude rod 39 and set by positioning cam 33, thenet effective force exerted on the pivoted arm 51 causes the contacts15, 16 to be cycled between their opened and closed position.

Many household temperature controls have a thermal lag, that is, theroom temperature precedes the control temperature. For this reason, whensuch a thermostat is set to respond between two predeterminedtemperatures, the temperature of the air in the house will overshoot andundershoot the predetermined temperatures. For this reason it is commonfor such thermostats to include a preheater, such as 71, mountedadjacent the bellows 43. The preheater 71 is connected by a pair ofleads 72 and 73 to connectors 74 and '75 respectively. The connector 74is connected to bus bar 19 while the connector 75 is connected to thebus bar 24 so that when contacts 15, 16 are closed to energize theheating system for the house the preheater 71 is also energized. Thiscauses the fluid within the thermostat to sense a temperature somewhathigher than the actual air temperature within the house. The thermostatthen will operate to de-energize the heating system before orcoincidentally as the air temperature within the house reaches thedesired operating temperature, of the thermostat, and thus eliminate thethermal lag of the control. It will be understood that, as the householdtemperature cools with the heating system off, the thermostat respondssubstantially directly to the air temperature within the house.

A second actuator 76 is provided with a shoulder 77 engaging theresilient contact strip 26 for contact 18. The other end 78 of theactuator 76 extends through appropriate openings in the arm 51 and theframe 29 and is disposed in proximity to the cam follower 31). Thus, themovement of the pivoted arm 51 controls opening and closing of thecontacts 15, 16 but does not affect the opening and closing of contacts17, 18. When the cam 33 is rotated so that the end 32 of the camfollower 30 drops in the notch 35, the cam follower will engage the ends69 and 78 of the actuators 65 and 76 and move them downwardly (as seenin FIG. 4) so as to cause both sets of contacts 15, 16 and 17, 18 to beopened in order to completely de-energize the system, regardless of thetemperature sensed by the fluid within the bellows 43.

With such condition responsive switch mechanisms or thermostats it isnecessary to have more force available than is necessary for movingcontact 16 between its opened and closed position with respect tocontact 15 to insure positive operation of the device. This excess forceis absorbed by engagement between various components such as between thearm 51 and the base 11 or frame 29 at the limits of movement of the arm51. These engagements cause noise which is undesirable, particularly inroom heating and cooling controls. The aforementioned Slonneger patentdiscloses a thermostat mechanism which uses thermal damping to controlthe instantaneous available force so as to provide sure but quietoperation. I have found that I can provide this thermal damping withoutincluding the sensing tube and bias heater arrangement of theexemplification thermostat shown in Slonneger and without'the necessityfor the care needed with the Slonneger exemplification to insure thatthe liquid portion of the fluid was confined to the sensing bulb.

Viewing particularly FIG. 3 it will be seen that the bellows 43 and cup44 provide a sealed thermally responsive expansible chamber. That is,the thermally responsive fluid is contained within an expansible chamberwhich does not have attached thereto any significant length of tubing orsensing bulb, the fill tube being pinched off very close to the bellowsso as to form, in effect, a portion of the bellows. It will be alsonoted from FIG. 3 that the thermally responsive fluid within the chamberis partially a liquid as indicated at 80 and partially a vapor asindicated at 81.

It will be understood that as the fluid comprised of the liquid 80 andvapor 81 changes temperature in response to changes in the sensedtemperature the vapor pressure of the fluid will change. This causesexpansion and contraction of a bellows and exerts a varying force on theoperator 39 for causing the contacts 15, 16 to be moved between theiropened and closed positions. I have found that by filling the expansiblechamber with a fluid, which is partially liquid and partially vapor, tothe extent that the change in vapor volume, as the bellows moves betweenits positions corresponding to contact open and contact closed, isrelatively large in comparison to the volume of the vapor at thebeginning of the movement in either direction there will be thermaldamping.

For instance, as the sensed temperature rises and the fluid rises intemperature, the liquid 80 tends to evaporate and form more vapor. Thisexerts a greater force on the operator 39 until the net force of thebellows 43 and range spring 37 is sufficient to cause arm 51 to pivotagainst the force of toggle spring 55 and contact strip 21 for openingcontacts l5, 16. As the contacts move open, the operator 39 moves to theright (as seen in FIG. 1) and the bellows expands. This expansion of thebellows increases the volume available for vapor within the expansiblechamber, which increase is relatively large compared to the beginningvapor volume. Temporarily the force exerted by the bellows decreasesuntil enough liquid has evaporated to provide sufficient vapor pressureto cause the bellows force to return to the necessary level. Thisincreased vapor pressure is available at the sensed temperature;however, it takes a significant period of time to develop. Thus, thereis thermal damping in the sense that the necessary force for moving thecontacts 15, 16 from their closed to their open position is availablewith time but is not instantaneously available and there is no build-upof excess force which would cause excess speed and attendant impactnoises.

A similar situation occurs as the sensing fluid cools and the contactsclose. As the contacts close, the bellows must contract. Thiscontraction of the bellows decreases the volume available for vaporwithin the expansible chamber, which decrease is relatively largecompared to the beginning vapor volume. Temporarily the force exerted bythe bellows increases until sufficient vapor has condensed to providethe desired reduced pressure. This decreased vapor pressure is availableat the sensed temperature; however, it takes a significant period oftime to develop. Thus thermal damping is provided both in the contactopening and the contact closing directions of operation of thethermostat.

By way of example, with a thermostat constructed generally as shown inthe drawings and including an expansible chamber having a volume ofabout 0.98 c.c. when depressed to a mechanical stop, a volume of about1.11 c.c. when contacts l5, 16 are closed and about 1.19 c.c. when thecontacts l5, 16 are open; and which mechanism includes the followingcharacteristics, as measured at the end of operator 39 having slot 49:contact gap between 0.004 and 0.007 inches, total travel between 0.014and 0.021 inches, a force differential of between 180 and 200 grams, acontact force between contacts l5, 16 of between 17 and 23 grams,friction in the mechanism of about 75 grams maximum and an excessiveavailable force of about grams; 1 found that the fill volume of theexpansible chamber, that is the bellows, should be greater than 0.55c.c. and less than 0.7 c.c. with best results being obtained with a fillof about 0.60 c.c. plus or minus 2 percent. Too small a fill produces acontrol with excessive noise and too large a fill produces a controlwith insufficient operating speed to insure proper action.

While in accordance with the Patent Statutes, I have described what atpresent is considered to be the preferred embodiment of this invention,it will be obvious to those skilled in the art that various changes andmodifications may be made therein without departing from the invention,and it is therefore aimed in the appended claims to cover all suchequivalent variations as fall within the true spirit and scope of theinvention.

I claim:

1. A condition responsive electric switch mechanism includm a. switchmeans having open and closed position;

b. switch actuating means connected to said switch means movable betweenfirst and second positions for operating said switch means between saidopen and closed positions;

c. spring means connected to said for transferring said switch closedswitch positions;

d. thermally responsive meansincluding a sealed expansible chamberassembly, connected to said switch actuating means for controllingmovement of said switch actuating means between said first and secondpositions in response to first and second predetermined temperatures;and

. said sealed expansible chamber assembly being partly filled withliquid and partly filled with vapor such that at least a 14 percentchange in the volume of vapor occurs as said switch actuating meansmoves between said first and second positions for producing thermaldamping to control the velocity of said switch actuating means as ittravels between said first and second positions.

2. A switch mechanism as set forth in claim 1 wherein: said switchactuating means includes a toggle mechanism exerting a force tending totransfer said switch means to one of its open and closed positions; saidspring means includes a range spring exerting a force tending totransfer said switch means to the other of its open and closedpositions; and means interconnects said toggle mechanism, said rangespring and said sealed expansible chamber assembly whereby a thermallydamped net effective force is provided to transfer said switch meansbetween its open and closed positions.

3. A switch mechanism as set forth in claim 2 wherein: said switch meansincludes a first set of contacts having open and closed positions; afirst actuator interconnects said toggle mechanism and said first set ofcontacts for transferring said first set of contacts between their openand closed positions; said switch means also includes a second set ofcontacts having open and closed positions; a second actuator is providedfor said second set of contacts; and manually actuatable means isprovided for selectively engaging both of said first and secondactuators for transferring both of said first and second set of contactsto their respective open positions.

4. A condition responsive electric switch mechanism including:

a. switch means having open and closed positions;

b. switch actuating means connected to said switch means movable betweenfirst and second positions for operating said switch means between saidopen and closed positions;

c. spring means connected to said switch actuating means fortransferring said switch means between open and closed switch positions;

d. thermally responsive means, including a sealed expansible chamberassembly, connected to said switch actuating means for controllingmovement of said switch actuating means between said first and secondpositions in response to first and second predetermined temperatures;

. said sealed expansible chamber assembly including a sealed expansiblechamber having a first internal spacial volume when said switchactuating means is in said first position and a second internal spacialvolume when said switch actuating means is in said second position; and

f. said sealed expansible chamber assembly being partly filled withliquid and partly filled with vapor with said vapor occupying a firstvapor volume within said first internal spacial volume and a secondvapor volume within said second internal spacial volume, said firstvapor volume being at least 14 percent greater than said second vaporvolume whereby thermal damping may be produced to control the velocityof said switch actuating means as it travels between said first andsecond positions. 1

5. A switch mechanism as set forth in claim 4 wherein: said switch meansincludes a toggle mechanism exerting a force tending to transfer saidswitch means to one of its open and closed positions; said spring meansincludes a range spring exerting a force tending to transfer said switchmeans to the other of its open and closed positions; and means interconnects said toggle mechanism, said range spring and said sealed switchactuating means means between open and expansible chamber assemblywhereby a thermally damped net effective force is provided to transfersaid switch means between its open and closed positions.

6. A switch mechanism as set forth in claim wherein: said switch meansincludes a first set of contacts having open and closed positions; afirst actuator interconnects said toggle mechanism and said first set ofcontacts for transferring said first set of contacts between their openand closed position;

1. A condition responsive electric switch mechanism including: a. switchmeans having open and closed position; b. switch actuating meansconnected to said switch means movable between first and secondpositions for operating said switch means between said open and closedpositions; c. spring means connected to said switch actuating means fortransferring said switch means between open and closed switch positions;d. thermally responsive means- including a sealed expansible chamberassembly, connected to said switch actuating means for controllingmovement of said switch actuating means between said first and secondpositions in response to first and second predetermined temperatures;and e. said sealed expansible chamber assembly being partly filled withliquid and partly filled with vapor such that at least a 14 percentchange in the volume of vapor occurs as said switch actuating meansmoves between said first and second positions for producing thermaldamping to control the velocity of said switch actuating means as ittravels between said first and second positions.
 2. A switch mechanismas set forth in claim 1 wherein: said switch actuating means includes atoggle mechanism exerting a force tending to transfer said switch meansto one of its open and closed positions; said spring means includes arange spring exerting a force tending to transfer said switch means tothe other of its open and closed positions; and means interconnects saidtoggle mechanism, said range spring and said sealed expansible chamberassembly whereby a thermally damped net effective force is provided totransfer said switch means between its open and closed positions.
 3. Aswitch mechanism as set forth in claim 2 wherein: said switch meansincludes a first set of contacts having open and closed positions; afirst actuator interconnects said toggle mechanism and said first set ofcontacts for transferring said first set of contacts between their openand closed positions; said switch means also includes a second set ofcontacts having open and closed positions; a second actuator is providedfor said second set of contacts; and manually actuatable means isprovided for selectively engaging both of said first and secondactuators for transferring both of said first and second set of contactsto their respective open positions.
 4. A condition responsive electricswitch mechanism including: a. switch means having open and closedpositions; b. switch actuating means connected to said switch meansmovable between first and second positions for operating said switchmeans between said open and closed positions; c. spring means connectedto said switch actuating means for transferring said switch meansbetween open and closed switch positions; d. thermally responsive means,including a sealed expansible chamber assembly, connected to said switchactuating means for controlling movement of said switch actuating meansbetween said first and second positions in response to first and secondpredetermined temperatures; e. said sealed expansible chamber assemblyincluding a sealed expansible chamber having a first internal spacialvolume when said switch actuating means is in said first position and asecond internal spacial volume when said switch actuating means is insaid second position; and f. said sealed expansible chamber assemblybeing partly filled with liquid and partly filled with vapor with saidvapor occupying a first vapor volume within said first internal spacialvolume and a second vapor volume within said second internal spacialvolume, said first vapor volume being at least 14 percent greater thansaid second vapor volume whereby thermal damping may be produced tocontrol the velocity of said switch actuating means as it travelsbetween said first and second positions.
 5. A switch mechanism as setforth in claim 4 wherein: said switch means includes a toggle mechanismexerting a force tending to transfer said switch means to one of itsopen and closed positions; said spring means includes a range springexerting a force tending to transfer said switch means to the other ofits open and closed positions; and means interconnects said togglemechanism, said range spring and said sealed expansible chamber assemblywhereby a thermally damped net effective force is provided to transfersaid switch means between its open and closed positions.
 6. A switchmechanism as set forth in claim 5 wherein: said switch means includes afirst set of contacts having open and closed positions; a first actuatorinterconnects said toggle mechanism and said first set of contacts fortransferring said first set of contacts between their open and closedposition; said switch means also includes a second set of contactshaving open and closed positions; a second actuator is provided for saidsecond set of contacts; and manually actuatable means is provided forselectivity engaging both of said first and second actuators fortransferring both of said first and second set of contacts to theirrespective open positions.